Sprinkle catfish with ¾ teaspoon salt and ½ teaspoon pepper. In a large saucepan, melt 1 tablespoon butter over medium-high heat. Add catfish; cook, turning once, until flaky and firm to touch, about 4 minutes per side. Remove from pan. Let stand for 5 minutes. Using 2 forks, shred catfish.
Reduce heat to medium. Add remaining 3 tablespoons butter to pan. Add onion; cook until tender, about 5 minutes. Add garlic; cook until fragrant, about 1 minute. Stir in flour; cook until bubbly, about 3 minutes. Gradually whisk in warm milk until smooth.
Remove from heat; stir in catfish, ½ cup bread crumbs, 2 teaspoons thyme, ½ teaspoon salt, and remaining ½ teaspoon pepper until well combined. Shape 2 tablespoonfuls of catfish mixture into small patties.
In a large Dutch oven, pour oil to a depth of 4 inches, and heat over medium heat until a deep-fry thermometer registers 350°.
In a shallow pan, place egg. In another shallow pan, combine remaining 1 cup bread crumbs, remaining 1 teaspoon thyme, and remaining ¼ teaspoon salt. Working in batches, dip croquettes in egg, letting excess drip off. Dredge in bread crumbs mixture, pressing gently to adhere.
Fry croquettes, turning as needed, until golden brown, 3 to 4 minutes. Remove using a slotted spoon, and let drain on paper towels. Serve with Chipotle Ranch. Garnish with thyme, if desired.
Chipotle Ranch
Place all ingredients in a blender; process until smooth. Cover and refrigerate for at least 1 hour or up to 1 week.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/catfish-croquettes/